This invention relates generally to a heterostructure device and to a method for its manufacture, and more specifically to a heterostructure field effect transistor (FET) having a high breakdown voltage and high mobility, and to a method for its manufacture.
There are many high frequency electronic applications, such as microwave power amplifiers, that require a high breakdown voltage to achieve high efficiency. Gallium arsenide (GaAs) field effect transistors, which are commonly employed for power amplifiers, typically exhibit breakdown voltages of less than 30 volts. To attain higher voltages while at the same time maintaining microwave frequency operation, it is desirable to employ alternative materials capable of sustaining higher breakdown voltages than can be obtained with GaAs. Some success has been achieved by using high field strength material such as silicon carbide (SiC) or aluminum gallium nitride (AlGaN). Devices manufactured using these materials, however, cannot be economically produced. Neither SiC nor AlGaN can be easily produced as large diameter wafers. The substrates are expensive and processing is difficult with the result that devices produced using these materials are expensive.
A need therefore exists for a transistor that can be used at microwave frequencies, that exhibits a high breakdown voltage, has a high mobility, can operate at high temperatures, and can be produced at low cost.